A variety of pumping systems are used on offshore drilling platforms to pump fluid such as oil and sea water. A conventional pumping system includes a horizontal motor coupled to a horizontal pump. The horizontal motor and pump are mounted to the deck of the drilling platform and used to pump fluids through appropriate conduits coupled to the pump. Such horizontal systems, however, require a relatively large area or "footprint" on the drilling platform. The large footprint is problematic because of the relatively severe space constraints on offshore drilling platforms.
An alternative to a horizontal system is a vertical pumping system mounted vertically on the offshore drilling platform. Vertical pumping systems employ a motor and a vertical pump connected by a motive power coupling. The internal components of a vertical pump, such as the impeller(s) and a rotatable drive shaft, are oriented vertically. Because of this vertical orientation, a vertical pumping system requires a smaller area (or "footprint") than a comparable horizontal pumping system. Because offshore drilling platforms have very limited deck space, the smaller footprint available with vertical pumping systems makes them better suited for use in offshore drilling platforms.
Vertical pumping systems employed to transfer fluids or to pump liquids from wells or deep drilled bore holes are comprised of a motor and a vertical centrifugal pump. Vertical turbine pumps are commonly used for this application. The motor drives a rotatable shaft in the vertical pump that is, in turn, connected to the impellers of the vertical turbine pump. The pump is mounted to the deck of the drilling platform, while the motor remains above the deck. As the motor rotates, the rotatable shaft rotates the impellers. As the impellers rotate they impart motion to the fluid.
The pump suction is located at the bottom of the pump and the fluid is drawn upward through the pump and the deck, and is discharged above the deck surface at or near the top of the pump. A mechanical seal is located around the rotatable drive shaft near the motor to act as a barrier to prevent fluid from leaking out of the pump around the shaft. The mechanical seal is thus exposed to fluid at pump discharge pressure on one side and, typically, atmospheric pressure on the other. The pump discharge pressure may be several thousand pounds per square inch greater than atmospheric or pump suction pressure. The mechanical shaft seal must be designed and manufactured to withstand the considerable strain placed on it by fluid at pump discharge pressure.
The present invention overcomes the problems of the prior art and provides an apparatus which employs a vertical pump in a manner which reduces the strain on the mechanical seal by exposing the mechanical seal to the lower pressure at the pump suction rather than the much higher pressure at the pump discharge.